The present invention relates to an incinerator and especially to an incinerator having primary and secondary incinerator chambers and sensor controlled air feed into incinerator chambers.
In the past, a wide variety of incineration devices and are usually classified as batch incineration or continuous incineration. Successive batch incineration methods typically utilize combustion in a primary combustion zone followed by an additional combustion with excess secondary air in a secondary combustion zone to ensure complete combustion and the elimination of smoke fumes and odors. Various techniques have been utilized for controlling the rates of primary and secondary air introduced into the primary and secondary combustion chambers and such techniques are generally such that the rate of secondary air is too high and overcooling of the combustion gas occurred in the secondary combustion chamber, especially during the loading of the primary chamber and during the incineration of each batch of waste material when the secondary combustion chamber is below operating temperature. Overcooling is uneconomical in that it waste heat which must be replaced by the burning of extra fuel and, in addition, does not provide sufficient complete combustion to eliminate all of the combustion particles and fails to meet regulatory requirements in the incineration of hospital and medical waste and the like.
In the past, incinerators have included primary and secondary combustion chambers which utilize temperature control and instruments to control the rates of both the primary and secondary air. The primary temperature controller senses the temperature of the combustion gases exiting the primary combustion chamber and adjusts the primary air rate according to control of the temperature of the combustion gases at the selected level. In a similar manner, a secondary air temperature controller senses the temperature of the combustion gases withdrawn from the secondary combustion chamber and adjusts the rate of secondary air to maintain the temperature of such gases at a relatively high selected temperature level. When such incinerators are being operated intermittently with time delays between batches of waste material or between groups of batches of waste material being incinerated, the high temperature level of the gases withdrawn from the secondary combustion chamber often cannot be maintained and overcooling in the secondary chamber takes place. Thus, the maximum rate and combustibility of combustion gases fed into the secondary combustion chamber occurs during the peak incineration stage of each waste batch so that the temperature of the combustion gases produced in the secondary combustion chamber cannot always be maintained at the selected high temperature level during loading and initial incineration steps and final incineration stage of each waste batch and the temperature of the combustion gas produced in the secondary combustion chamber fall below the required or desired temperature level as a result of the intermittent incinerator operation.
Prior U.S. patents which show various waste incinerators and methods of incineration includes the Wright et al. U.S. Pat. No. 4,870,910, in which the rate of secondary air combined with combustion gases in the secondary combustion zone is controlled to maintain the combustion gases withdrawn therefrom at a substantially constant selected temperature level during the peak incineration stage of each waste batch. The air is controlled by temperature sensors along with timer controlled switches to vary the flow of air. In the Lewis U.S. Pat. No. 4,453,474, a method for controlling temperatures in the afterburner of a multiple hearth furnace modulates the amount of combustion air and controls the temperature of the afterburner within certain predescribed limits by splitting the feeding of sludge between waste material handling hearths. The Martin U.S. Pat. No. 4,953,477, shows a method and apparatus for regulating the furnace output of incineration plants which measure the combustion temperature, the flame radiation, or the brightness in the respective combustion zones which are compared with preselected standard values and regulate the flaps in the air supply pipes to guide the combustion air to the individual combustion, zone. The Haftke et al. U.S. Pat. No. 4,635,567, shows a monitoring of the burner operations in a burner using pulverized fuel entrained in the air and controls the combustion by adjustment of the secondary air flow to each of three burners. The rate of flow of the primary and secondary air are determined and a photodiode measures the temperature of the burner flame. The Gitman et al. U.S. Pat. No. 4,861,262, is a method and apparatus for waste disposal which varies the flows of at least two oxidizing gases and . auxiliary fuel in both the primary incinerator and afterburner so as to operate the system under fluxuating waste loading conditions. The Leffler et al. U.S. Pat. No. 4,359,950, is a method of maximizing the reduction efficiency of a recovery boiler by varying the amount of air entering into the boiler through the primary air input until the minimal amount of sulpher dioxide is measured at the exhaust output.
The present invention, on the other hand, is directed at batch incineration of medical and hospital waste materials and the like which requires a predetermined temperature in the secondary incineration chamber and in which a simplified control uses separate ultraviolet detectors in predetermined positions to measure the length of the flame in the secondary chamber and then to individually control a plurality of secondary air inputs responsive to the position of the flame sensed by the ultraviolet sensor. This makes for a reliable and accurate control system to meet the regulatory requirements for a more complete combustion.